Reaction mixture 1 ml of pg 05 ml of 10 vv hno3 1 ml

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Reaction mixture: 1 mL of Pg, 0.5 mL of 10% (v/v) HNO3, 1 mL of water, and 1 mL of 2 mM Mn(IV), (injected). a. Full range; b. Lower concentrations.
89 color of the 20 mM solution did not change during storage overnight; however, the CL signals of ethanol and Pg with the aged solution were about 20% greater compared to that obtained with the fresh solution. The color of the 2 mM Mn(IV) solution turned pink during overnight storage and no CL signal observed upon injecting the aged solution. With the fresh 2 mM Mn(IV) solution, both the Pg and ethanol signals decreased (by about 25 and 30%, respectively) with the addition of 1 M Mn(II). The fresh solution was pale yellow and it gave a higher signal with 100 AM Pg than the 20 mM solution. Possibly the more concentrated solution which is dark in color absorbs more of CL radiation. Optimization with Mn(III) as the Oxidant Mn(III) was injected into reaction mixture of Pg instead of permanganate. HNO3 and Mn(III) concentrations were optimized for 100 AM Pg and 10% (v/v) ethanol. The Mn(III) stock solution was prepared in 50% (v/v) H2SO4 and all solutions were diluted with 50% H2SO4. Even with a lower acid concentration than used in previous studies (90% (v/v)), the solution is very viscous and it was difficult to keep the injected volume constant. The optimum acid concentration for Pg was 1% (v/v) and that of Mn(III) was 25 mM. A calibration curve for Pg with Mn(III) is shown in Figure 22. For ethanol, the optimum acid concentration was 100% (v/v) and that of Mn(III) was 25 mM.
90 900 803-700-E 600-503-co (7) (7 400-300-200 100 0 o 500 woo 1500 2000 2E00 [PO] (uM) 3000 3503 4003 250-100 50-0 0 1.0 20 30 40 50 60 70 80 90 100 [Pg] (uM) Figure 22. Calibration curve for Pg with Mn(III) as the oxidant. Reaction mixture: 1 mL of Pg, 0.5 mL of 1% (v/v) HNO3, 1 mL of water, and 1 mL of 25 mM Mn(III), injected. a. Full range; b. Lower concentrations.
91 A calibration curve for ethanol with Mn(III) is shown in Figure 23. The detection limits for ethanol and Pg were calculated to be 0.2% (v/v) and 0.4 LM, respectively. Comparison of Mn04, Mn(IV) and Mn(III) as Oxidants Table 13 shows a comparison of KMnO4, Mn(IV) and Mn(III) as oxidants for Pg and ethanol. The concentration for all three forms of the Mn oxidant was adjusted to be the same to allow comparison. The 1 mM oxidant concentration is considerably less than the optimum for Mn(III) and may account for the absence of a CL signal. Table 13. Comparison of Mn04, Mn(IV) and Mn(III) as Oxidants for Pg and Ethanol Pg Signal (mV)' Et0H Signal (mV) MnOi Mn(IV) MnOi Mn(IV) Mn(III) 87.2 3.4 148 180 52.8 78.9 3.7 145 179 43.3 82.7 3.9 151 174 48.7 89.0 3.1 152 182 45.1 88.6 2.9 155 180 50.9 86.3 3.1 150 184 51.3 Avg 85.5 3.4 150 180 48.7 SD 3.6 0.4 3.3 2.9 3.4 * no signal for Pg with Mn(III). Reaction mixture for Pg: 1 mL of Pg (100 AM), 0.5 mL of acid (10%) and 1 mL of oxidant (1 mM) injected. For ethanol: 1 mL of ethanol (10%), 0.5 mL of acid (100%) and 1 mL of oxidant (15 mM) injected.
92 1 30 40 io650 70 [EtOH] (% (v/v)) Figure 23. Calibration curve for ethanol oxidant.

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